The present invention relates to a new and improved method of, and apparatus for, regulating the rotational speed of an electric motor operated in the four quadrant mode of operation.
In its more particular aspects, the present invention specifically relates to a new and improved method of, and apparatus for, regulating the rotational speed of an electric motor operated in the four quadrant mode of operation and in which method and apparatus there is provided a regulating unit with which the electric motor is series connected and which supplies variable power to the electric motor.
For regulating the rotational speed, namely the number of revolutions per unit of time, of an electric motor intended for the four quadrant mode of operation it is standard practice to derive from the electric motor two tachometer data and to compare such two tachometer data with predetermined reference values. Deviations between the thus derived tachometer data and the reference values result in generally known actions on the regulation circuit. As the tachometer data there are conventionally provided two signals having a magnitude which is proportional to the rotational speed of the electric motor. From these two signals there can also be derived the rotational direction of the electric motor. In this manner there is rendered a reliable regulation of the electric motor such that there do not occur any operating states which could lead to inappropriate regulatory actions.
It is one disadvantage of this known regulation method for regulating electric motors such that a predetermined rotational speed is maintained at high precision, that the necessary tachometers for obtaining the two tachometer data concerning rotational speed and rotational direction, are complex and very expensive. It is well known that this is increasingly so with increasing precision requirements.
A circuit for stabilizing the speed of a DC-motor is known, for example, from U.S. Pat. No. 3,944,901, granted Mar. 16, 1976. The DC-motor is connected with a tachometer and an amplifier for controlling the DC-motor. A resonant circuit is interconnected between the output of the tachometer and the input of the amplifier and suppresses interfering frequencies in the output signal of the tachometer and furthermore amplifies the output signal of the tachometer.
It is one disadvantage of this circuit that such circuit is unsuitable for regulating the rotational speed of the DC-motor through a wide range of rotational speeds. The reason is that the resonant circuit can be laid out only for one frequency, namely the resonant frequency. When operation is desired in a number of quadrants, this circuit also requires an additional tachometer signal indicating the running direction.